Freezing point lowering compositions are in widespread use for a variety of purposes, especially to reduce the freezing point of an aqueous system so that ice cannot be formed or to melt formed ice. Generally, freezing point lowering compositions depend for their effectiveness upon the molar freezing point lowering effect, the number of ionic species that are made available and the degree to which the compositions can be dispersed in the liquid phase in which the formation of ice is to be precluded and/or ice is to be melted.
The most pervasive of the commonly used products for deicing are common salt, calcium chloride and urea, with common salt (sodium chloride) being the least expensive and most commonly used. Common salt is widely used to melt ice on road surfaces and the like. In this manner the salt forms a solution with the available liquid in contact with the ice and thereby forms a solution with a lower freezing point than the ice itself so that the ice is melted. Chloride salts however suffer from relatively severe drawbacks, such as the harmful effects on surrounding vegetation by preventing water absorption in the root systems, the corrosive effects on animal skin such as the feet of animals, clothing, roadways and motor vehicles, and the deleterious effects on surface and ground water. Thus, any new method of deicing or new deicing composition that can reduce the amount of chloride salts would solve a long felt need in the art.
For example, in roadway deicing applications, liquid calcium chloride (32%) is typically the preferred material when temperatures are too low for rock salt to be effective. However, the use of chloride salts often is not permitted or needs to be reduced in certain areas because of its highly corrosive nature, which causes destruction of surrounding vegetation, damage to roadways and vehicles, and contamination of water supplies.
Another drawback of certain prior art deicing fluids is the high chemical and biological oxygen demand that make them environmentally unfavorable. The glycols are exemplary of deicing fluids that particularly suffer from this type of environmental drawback. Thus, any new method of deicing or new deicing composition that can reduce the amount of glycols would solve a long felt need in the art.
Due to the problems associated with deicing agents as described above, there have been attempts to prepare even more deicing agents. For, example, Kaes, U.S. Pat. No. 4,448,702, discloses the use of a freezing-point lowering composition and method that calls for the addition of a water-soluble salt of at least one dicarboxylic acid having at least three carbon atoms, such as a sodium, potassium, ammonium or organoamine salt of adipic, glutaric, succinic or malonic acid.
Peel, U.S. Pat. No. 4,746,449, teaches the preparation of a deicing agent comprising 12-75% acetate salts, trace-36% carbonate salts, 1-24% formate salts and 1-32% pseudolactate salts that is prepared from a pulp mill black liquor by fractionating the black liquor into a low molecular weight fraction and concentrating the collected low molecular weight fraction to produce the deicing agent.
U.S. Pat. No. 4,960,531 teaches that small amounts of methyl glucosides, i.e., less than 10%, in combination with a low amount, i.e., about 2.5%, of potassium carbonate can be employed as a trigger to conventional salt deicers. The '531 patent is an improvement patent on U.S. Reissue Pat. No. RE 32,477 that teaches the use of a salt mixture of sodium and potassium chloride and an amide. Other inorganic salts are also known to be useful as freezing point lowering agents such as magnesium chloride, potassium phosphates, sodium phosphates, ammonium phosphates, ammonium nitrates, alkaline earth nitrates, magnesium nitrate, ammonium sulfate, and alkali sulfates.
Special mention is also made of Sapienza, U.S. Pat. No. 5,876,621 and Sapienza, U.S. Pat. No. 5,980,774 that disclose especially useful deicing and anti-icing compositions.
Solutions of low freezing point deicing and anti-icing agents typically include brines, ethylene glycol and propylene glycol solutions. The use of brines in anti-icing compounds can reduce, although not eliminate, the impacts of chlorides. Brines are used to transfer heat at temperatures below the normal freezing point of water. Ethylene glycol solutions are well known for use as coolants for automobiles and the like in regions in which the temperature may fall below the normal freezing point of water. Ethylene and propylene glycols are used in relatively large quantities at major airports in northern climates in order to keep air traffic flowing during inclement weather. The fluids generally are applied to the wings, fuselage and tail of aircraft as well as the runways to remove ice. However, these glycol compounds likewise have environmental drawbacks and can be detrimental to sewage treatment processes.
Other prior art deicing fluids, such as alcohols, have toxic effects and high volatility particularly in the low molecular weight range and may be the cause of offensive smell and fire danger. Furthermore, mono- and polyhydric alcohols oxidize in the presence of atmospheric oxygen to form acids, which can increase corrosion of materials.
Yet another reason why new deicing fluids are needed emerges from the recent changes to the freezing point requirements of the SAE AMS 1435A specification for airport runway deicing fluids. Newer AMS 1435A specifications require deicing fluids to have a freezing point of less than −14.5° C. for a 1:1 weight dilution. These specifications are such that many technologies, including existing glycol-based fluids currently used commercially, no longer meet the new requirements, including ASTM D 1177.
As such there exists in the art a need for new and improved deicing and/or anti-icing agents. Preferably these are free or substantially free of inorganic salts, are environmentally benign and are prepared from relatively inexpensive raw materials while still possessing desirable freezing point depression properties. Likewise, there also exists a need in the art for new deicing and/or anti-icing agents that can be used in combination with prior art deicing agents, such as inorganic salts or glycols, to substantially reduce the amount of inorganic salts or glycols, and thereby concomitantly reduce the environmental affects of the salts and/or glycols. Surprisingly, it has been found that compositions disclosed herein meet these needs.
The total active composition of the new deicing and/or anti-icing agents can vary from about 5 to about 100 weight percent. Improved solid deicers can be prepared that can be applied in the same manner as solid chloride salts with the environmental advantages described earlier.